1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copying machine, printer and the like, having a member capable of contacting with an image bearing member.
2. Related Background Art
In the past, it is known to transfer a toner image formed on a rotatable photosensitive drum as an image bearing member onto a sheet-shaped transfer material passing between the photosensitive drum and a transfer roller (contact member) urged against the photosensitive drum. In this case, a voltage having the reverse polarity opposite to the polarity of the toner is applied to the transfer roller to electrostatically attract the toner image to the transfer material.
Normally, the transfer roller is formed from elastic material such as rubber. In this case, however, since the photosensitive drum is directly urged against the transfer roller, the rubber powder of the transfer roller and/or the filler in the rubber adhere to the photosensitive drum. Such materials accumulate in the proximity of a cleaning blade for cleaning the photosensitive drum after the transferring operation and sliding access the surface of the drum. Therefore, such accumulated materials cause damage to the photosensitive drum and generate black stripes and white stripes in the image after several thousand transfer operations. Further, if the printing operations are on transfer materials having a small width in a direction perpendicular to a moving direction of the transfer material are repeated, since areas of the photosensitive drum which are not in contact with the transfer material are always rubbed by the transfer roller, the wear amount of such areas at the position of the cleaning blade is greater than that the area of the photosensitive drum which is in contact with the transfer material. Thereafter, for example, if the printing operation for a large-sized transfer material is performed, there will arise a difference in image density between the areas of the drum which are not in contact with the small-sized transfer materials and the area of the drum which is in contact with the small-Sized transfer materials, thereby creating a poor image.
Further, since the transfer drum urges the transfer material against the photosensitive drum at the zone of the photosensitive drum which is contacted with the transfer material in a generatrix direction of the photosensitive drum, paper powder from the transfer material (paper sheet) adheres to the photosensitive drum and accumulates in the proximity of the cleaning blade. Also if such paper powder rubs against surface of the photosensitive drum, it is feared that the drum is damaged and the black and white stripes are formed in the image.